Memory impairments associated with hippocampal versus parahippocampal-gyrus atrophy: an MR volumetry study in Alzheimer's disease.

Delayed memory impairments and medial temporal-lobe atrophy are considered to be cardinal features of Alzheimer's disease (AD). The goal of the present magnetic resonance (MR) volumetry study was to investigate the relationship between both features. We determined MR-derived estimates of hippocampal and parahippocampal volume in a sample of 27 AD patients and in a group of 26 healthy control subjects (NCs) of comparable age and education. We examined the performance of the two groups on immediate and delayed recall trials of an auditory-verbal list-learning task (CVLT), a visual non-verbal memory task (Visual Reproduction of the WMS-R), and a screening procedure that provides an estimate of overall cognitive functioning (DRS). Volumes of the hippocampus and the parahippocampal gyrus were significantly smaller in AD patients than in NCs. AD patients were impaired in their overall level of cognitive functioning and showed memory deficits under immediate and delayed recall conditions. The association between medial temporal-lobe atrophy and cognitive impairments in AD was found to be highly specific: Hippocampal volume correlated positively with delayed but not immediate recall of the verbal auditory list learning task. In contrast, parahippocampal gyrus volume, specifically in the right hemisphere, was positively related to delayed but not immediate recall of the non-verbal visual memory task. In NCs, there was a trend towards a negative association between hippocampal volumes and delayed verbal recall. Our results suggest that hippocampal and parahippocampal gyrus atrophy in AD are related to distinct aspects of the patients' memory impairments. Our findings have implications for current discussions regarding contributions of the hippocampus and the parahippocampal gyrus to memory in the intact human brain.